This is a Ruby tree! It shows every object from the Ruby Programming Language in a tree format.

<< 

        # Array.<<

(from ruby core)
---
    array << object -> self

---

Appends `object` to `self`; returns `self`:
    a = [:foo, 'bar', 2]
    a << :baz # => [:foo, "bar", 2, :baz]

Appends `object` as one element, even if it is another Array:
    a = [:foo, 'bar', 2]
    a1 = a << [3, 4]
    a1 # => [:foo, "bar", 2, [3, 4]]

This is MURDOC! A Ruby documentation browser inspired by Smalltalk-80. It allows you to learn about Ruby by browsing through its class hierarchies, and see any of its methods.